1. Field of the Invention
The present invention relates to an automatic control device for an air compressor, more particular, to an automatic control device for an air compressor, which lowers down the waste of energy and avoids damages to the motor of the air compressor.
2. Description of Related Art
A conventional air compressor drives a motor to run for pumping air into an air tank when the air pressure in the air tank is lower than a preset low value such as 5 kilograms per square centimeters, and stops pumping air into the air tank with the motor in idle running when the air pressure therein reaches a preset high value such as 7 kilograms per square centimeters. The air pressure in the air tank shall be decreased due to the use of the air compressor and whenever it reaches the preset low value, the compressor starts to pump air into the air tank again. This procedure shall repeat for maintaining the air pressure in the air tank between the preset high and low values. This conventional air compressor is said to be operating in a heavy-running mode when it is pumping air into the air tank and in an idle-running mode when it stops pumping air into the air tank.
The previous conventional air compressor operating in such an idlerunning/heavy-running mode suffers a disadvantage in waste of energy because the motor is in idle running when the air compressor does not pump air into the air tank. To overcome this disadvantage, a second conventional air compressor operating in an auto-stop/start mode is provided. Similarly, this second conventional air compressor drives a motor to run for pumping air into an air tank when the air pressure in the air tank is lower than the preset low value. However, it stops pumping air into the air tank by stopping the motor when the air pressure in the air tank reaches a preset high value. When the air pressure in the air tank is decreased and has reached the preset low value, the compressor starts to pump air into the air tank again by restarting the motor. This procedure shall repeat for maintaining the air pressure in the air tank between the preset high and low values. This second conventional air compressor operating in the auto-stop/start mode avoids the waste of energy because the motor is stopped when the air compressor does not pump into the air tank. Unfortunately, the times that a motor can be restarted is restricted, for example six times per hour, in order to avoid over-heating to the coil of the motor and hence, the air compressor operating in the auto-stop/start mode is not satisfactory. Therefore, there is a continuing need for the above air compressors to be improved.